Dual Vent

Dual venting is a type of group venting where one vent protects two fixture traps.

   Dual vented fixtures must connect to vertical drainage piping. 

Fittings for installation dual vent  Table 7.2.4.5.:

Double Sanitary T or Short Turn Double TY	Restrictions      accepted only if vertical run is of 3" size or larger and horizontal branches are of 1 1/4", 1 1/2" or 2" size.
Double Combination Y and 1/8 Bend or Double Long Turn TY	No restrictions
Double Y & two 450 elbows	No restrictions
Double Waste Fitting	Restrictions      accepted only if vertical run is of 3" size or larger and horizontal branches are of 1 1/4", 1 1/2" or 2" size.

Dual vented fixtures may have different flood level rims and different sized fixture drains.

7.4.8.2.(1):

"the maximum length of a fixture outlet pipe of any fixture is 900 mm".

There is no minimum length requirements for a fixture outlet pipe. This means that two different fixtures may be dual vented and connect at the same level with a double Y and two 450 elbows.

Part 7 places no conditions, restrictions or installation requirements of any kind on dual vented installations.

Drain Pipe Sizing:

The size of the vertical drainage piping serving a dual vent is determined by the size of outlet pipes of the dual vented fixtures and the total fixture unit load.

 See Drainage System Pipe Sizing 

Vent Pipe Sizing:

7.5.7.2.(2) states that a dual vent is sized as a branch vent according to Table 7.5.7.2. A.